Thanks to their advantages in thickness, weight, power consumption and the like, liquid crystal displays have widely been diffused as displays for word processors, computers, navigation systems and so on. Concurrently with this, liquid crystal displays have become able to reproduce high-quality and colored images.
Among others, one type of those liquid crystal displays has been particularly popular, that is, active matrix liquid crystal displays, in which pixels are disposed in a matrix manner, and as a switching element, an active element such as a thin film transistor is provided in each pixel, have become mainstream.
A typical active matrix liquid crystal display includes a first glass substrate provided with scanning lines, gradation signal lines, switching elements, and pixel electrodes, and a second glass substrate provided with a black matrix, color filter, and common electrode. These first and second glass substrates face each other with a certain space in between, and this space is filled with a liquid crystal material and the periphery of the space is sealed using a thermosetting or photo-setting sealing material. In each pixel, gradation image reproduction is realized by controlling a voltage between a pixel electrode and common electrode.
As multi-scene displays, mobile liquid crystal displays typified by mobile phones and PDAs (Personal Digital Assistants) are supposed to be used in various circumstances both in indoors and outdoors. For such a multi-scene display, a display panel which can carry out both reflective image reproduction and transmissive image reproduction has been proposed.
When such a display panel carries out reflective image reproduction with a color filter optimized for transmissive image reproduction, outside light passes through the color filter twice, namely on the occasion of entry and on the occasion of exit, so that the quantity of light as a result of reflection is extremely low. On the other hand, when transmissive image reproduction is carried out with a color filter optimized for reflective image reproduction, the range of color reproduction is extremely narrow. In both cases, the quality of images reproduced by the display deteriorates.
To solve this problem, for instance, Japanese Laid-Open Patent Application No. 11-305248/1999 (Tokukaihei 11-305248; published on Nov. 5, 1999) teaches, as shown in FIG. 14, the use of a color filter 100 including first color filters 101 and second color filters 102, each pair of the filters being of different chromaticity. In the color filter 100, respective pairs of the first color filters 101 and second color filters 102 are provided for colors of R (red), G (green), and B (blue). The chromaticity of the first color filters 101 is set so as to be identical with the chromaticity indicated by a chain line a in the chromaticity diagram in FIG. 15, and the chromaticity of the second color filters 102 is set so as to be identical with the chromaticity indicated by a dashed line b in the chromaticity diagram in FIG. 15.
In a liquid crystal display adopting the color filter 100, the first color filters 101 are associated with transmissive image reproduction, and the second color filters 102 are associated with reflective image reproduction. This realizes that a color of the light for transmissive image reproduction, which passes through the first color filters 101 once, is substantially identical with a color of the light for reflective image reproduction, which passes through the second color filters 102 twice.
The color filter 100 described above is conventionally formed by a pigment-dispersed photoresist method. The steps of manufacturing the color filter 100 by the pigment-dispersed photoresist method are as follows: A photoresist (color resist) in which a pigment is dispersed is applied to a substrate, and the applied color resist is exposed to light with a predetermined exposure pattern and developed, so that the color resist is removed except those parts to be the first color filter 101. As a result, the first color filter 101 is formed. The second color filter 102 is also formed in a similar manner. In this way, respective pairs of the first and second color filters 101 and 102 are formed for the colors of R, G, and B.
Meanwhile, being different from the pigment-dispersed photoresist method, for instance, Japanese Laid-Open Patent Application No. 5-273410/1993 (Tokukaihei 5-273410; published on Oct. 22, 1993) proposes a method of forming a color filter by a coloration using polysilane. According to this method, a polysilane layer is selectively exposed to ultraviolet light so that a latent image of a coloration pattern is formed on the polysilane layer, and this polysilane layer with the latent image of the coloration is soaked in a coloring colloidal solution made of metal alkoxide and including a pigment, and then dried. As a result, that part of the polysilane layer where the latent image is formed is colored so that this colored part can be utilized as a color filter.
However, when the color filter 100 which is shown in FIG. 14 and includes the pairs of the first and second color filters 101 and 102 of different chromaticity, the pairs corresponding to the respective colors of R, G, and B, is formed using a conventional pigment-dispersed photoresist method, both the step of forming the first color filter 101 and the step of forming the second color filter 102 have to be repeated twice in order to form one pair of the first and second color filters 101 and 102, and these steps further have to be repeated in order to form the pairs corresponding to the respective colors of R, G, and B. Thus, it is necessary to carry out the forming steps for 2×3=6 times. As a result, the number of the steps increases.
In each of the foregoing forming steps, furthermore, the color resist is applied, patterned and then removed except necessary parts. On this account, since the number of times the forming steps are carried out is large, an amount of the color resist removed as unnecessary parts is also large. As a result, a large amount of resist material is required for forming the color filter, so that the materials cost increases.
Moreover, when the pigment-dispersed photoresist method is used, it is difficult to manufacture the color filter 100 having the shape shown in FIG. 14, so that the color filter 100 would actually be shaped as in FIGS. 16(a)-16(c). Note that, the arrangement of the first and second color filters 101 and 102 in FIGS. 16(a)-16(c) is different from that of FIG. 14, for the sake of convenience.
As in FIG. 16(a), the first and second color filters 101 and 102 formed by the pigment-dispersed photoresist method are longitudinally tapered. For this reason, a gap g is formed between the neighboring first and second color filters 101 and 102.
Further, as illustrated in FIG. 16(b), a level difference d may be formed between the first and second color filters 101 and 102, due to the difference in thickness when these filters are formed.
As FIG. 16(c) shows, when the first and second color filters 101 and 102 are misaligned on the occasion of the patterning, for instance, a non-film portion v and a multiple-film portion w may be formed in the second color filter 102. Generally, the formation of these portions is caused by the misalignment of 3-5 μm.
As described above, these gap g, level difference d, non-film portion v, and multiple-film portion w cause the leakage of light and a domain is produced, and thus causing the quality of reproduced images to deteriorate.